The present invention relates to light guides, and more particularly, to light guides based on liquid crystals.
Data communication systems based on fiber optics provide substantially higher bandwidth than systems based on electrical systems. Unfortunately, switching devices for switching optical signals between an input fiber and a plurality of output fibers have not kept pace. As a result, optical signals are typically converted back to electrical signals prior to switching. The electrical signals are then switched using conventional packet switching techniques and reconverted to optical signals prior to entering the output fibers. The limitations of electrical switching systems prevent the realization of the full data bandwidth of the fibers. Accordingly, a significant amount of research has gone into developing optical switches that avoid the conversion of the light signals back to electrical signals.
One promising method for switching optical signals between optical paths relies on a waveguide whose location is electrically controlled. A waveguide may be generated by altering the index of refraction of a medium along the path over which the light is to travel such that the desired path has a higher index of refraction than the surrounding medium. Devices based on liquid crystals are particularly attractive because of the large change in index of refraction for light of a predetermined polarization that can be induced in a liquid crystal layer by applying a low frequency AC electrical field across the layer. A simple switching device can be constructed by energizing one set of electrodes on the surface of the liquid crystal layer while leaving an alternative set in a non-energized state. The region between the energized electrodes then becomes the waveguide that specifies the direction in which the light signal will propagate in the liquid crystal layer.
The AC field across the layer must be maintained to maintain the light path. If power is interrupted, the waveguide will disappear and the device will cease to operate. This increases the power requirements associated with the optical path and prevents the deployment of such light guides at system locations that are subject to power failures.
Broadly, it is the object of the present invention to provide an improved optical switching element.
It is a further object of the present invention to provide an optical switching element that does not require power to be continually applied in order to operate.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
The present invention is a bistable switchable waveguide having first and second states. The waveguide guides light along a predetermined path in the first state while providing no guiding of the light in the second state. The waveguide includes a guide layer constructed from a layer of a material having a first index of refraction when the molecules of the material are aligned in a first direction and a second index of refraction when the molecules are aligned in a direction orthogonal to the first direction. The guide layer is sandwiched between first and second surfaces that are in contact with the guide layer. The first surface causes the molecules of the guide layer adjacent to the first surface to be aligned in the first direction. The second surface has first and second regions in which the second surface causes the molecules of the guide layer adjacent to the second surface to be aligned in the first direction. The second surface also includes a third region in which the second surface causes the molecules of the guide layer adjacent to the second surface to be aligned in a second direction. The waveguide has first and second electrodes for causing the molecules of the guide layer to be aligned in a second direction that is the second direction in a region bounded by the third region and the first surface. The waveguide may also includes third and forth electrodes for causing the molecules of the guide layer to be aligned in a direction parallel to the first direction in a region bounded by the third region and the first surface. The guide layer is preferably constructed from a liquid crystal material.